Dr. Universe: How did the first drop of water ever happen on Earth?

-Ash, 6, SeaTac, WA

Dear Ash,

We’ve learned a lot about how water supports life on the blue planet, but the first drop is a bit mysterious. Scientists have a few theories about how it happened.

My friend Jen Adam co-leads the State of Washington Water Research Center. She told me the answer really goes “beyond physics.” She introduced me to her friend Michael Goldsby, a philosopher of science. Adam and Goldsby work together at Washington State University studying climate change and water.

Earth’s water covers three-fourths of the planet, but is made up of just two substances: hydrogen and oxygen. So, if you want to know where the first drop came from, you’d want to start with them.

“Once again, there’s the simple answer,” Goldsby said. “When the conditions are right, oxygen and hydrogen get together and form water. But then we get to the next question. When did hydrogen and oxygen form?”

Goldsby said the answer brings us back to the theory that most atoms and elements, including hydrogen and oxygen, formed around the time of the Big Bang—when all matter was in a single point that exploded. It sounds unbelievable, but there’s lots of evidence to support that theory.

dru-hero-poseHydrogen is the smallest element and appeared near the beginning of the universe. Heavier elements, including oxygen, came from the inside of extremely hot stars. When stars die, they become supernovae and explode. The explosion releases elements, including oxygen, back into space. Hydrogen probably waited a while to find oxygen from a star to create water molecules.

“Science relies on evidence we gain from observations and experiments,” Goldsby said. “Since we can’t observe what it was like before the Big Bang, we can only guess—although some guesses might be better than others.”

Some scientists have gathered evidence that suggests water was already around when Earth formed billions of years ago. At the time, young Earth was part of a scorching hot environment. So, the liquid water might have evaporated into space.

Other scientists have suggested that water came from deep inside Earth, up through volcanoes, and moved freely into the air. It’s uncertain how molecules would have returned to the planet’s surface to fill oceans.

Scientists also searched for evidence in some of the oldest objects in the solar system, icy meteorites. They’ve been looking really hard at a kind called carbonaceous chondrites. They are packed with frozen water. During Earth’s younger years, these formed far enough away that they could stay frozen outside the Earth’s hot environment. When the Earth cooled down, chondrite meteorites could have hurled their way to the Earth’s surface. It would have taken quite a lot of meteorites to fill the ocean.

So, I’m a bit stumped on this answer, Ash. You asked a great question. Water is what supports life here on Earth and it has for billions of years. I think if other cats understood the importance of science and water, they’d have more appreciation for baths.

Dr. Universe